Add Prevent Mailer Previews From Cluttering Database as a Rails TIL

rails/prevent-mailer-previews-from-cluttering-database.md

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+# Prevent Mailer Previews From Cluttering Database
+
+ActionMailer Previews give you a way to view email templates that your system
+sends. This is how I check that it is styled properly and that the logic and
+data of the template are able to run and render.
+
+Data for a preview typically means we need ActiveRecord objects and even their
+associations. If we start creating one-off records in our previews either with
+`#create` or with something like `FactoryBot`, those records will get left
+behind in our development database. Every view and refresh of a preview will
+generate more of these records.
+
+One way to get around that is to use `#new` and `#build`. I've found this
+cumbersome and it often leaves assocations missing or inaccessible.
+
+What if instead the preview could clean up after itself? That sounds like a
+great job for a database transaction.
+
+Let's create a `test/mailers/previews/base_preview.rb` as a base class for all
+our preview classes.
+
+```ruby
+class BasePreview < ActionMailer::Preview
+  def self.call(...)
+    message = nil
+    ActiveRecord::Base.transaction do
+      message = super(...)
+      raise ActiveRecord::Rollback
+    end
+    message
+  end
+end
+```
+
+This wraps the existing `self.call` functionality in a transaction that
+collects the resulting message from the preview and then rolls back the
+database changes.
+
+Now, instead of our individual preview classes inheriting directly from
+`ActionMailer::Preview`, they can inherit from `BasePreview`.
+
+```ruby
+class UserMailer < BasePreview
+
+  # ...
+
+end
+```
+
+[source](https://stackoverflow.com/a/31289295)